KR0179671B1 - Ethylene glycol recovery process - Google Patents

Abstract

The present invention relates to an improved process for recovering ethylene glycol from waste glycols produced in the production of polyethylene terephthalate. Waste glycol typically consists of metal oxide catalyst residues, low molecular weight terephthalate oligomers, diethylene glycol and other trace impurities. The improved process of the present invention increases the solubility of low molecular weight oligomers by increasing the temperature of the waste glycols so as to dissolve them in low molecular weight ethylene glycol and to reduce waste glycols at elevated temperatures to filter (5), activated carbon (6) and cations (7). ), Based on the principle that metal oxide catalysts, colored impurities and other trace impurities can be removed by passing through an ion exchange layer of anion (8) and mixed resin (9).

Description

[Name of invention]

Ethylene Glycol Recovery Method

Detailed description of the invention

[Technical Field]

The present invention relates to a method for removing impurities present in ethylene glycol recovered from a process for producing polyethylene terephthalate (PET).

Background Technology

PET is generally obtained by esterifying derephthalic acid (TPA) with excess ethylene glycol (EG) or transesterification of dimethyl terephthalate (DMT) with excess EG to obtain polyhydroxy ethyl terephthalate (DHET). (1) and linear polyester produced in two steps by step (2) polycondensing DHET in the presence of a metal oxide. Metal oxide catalysts are typically antimony oxides.

The first stage ester reaction requires an excess of EG. Excess EG is removed during the reaction which is polycondensed with other products such as low molecular weight terephthalate oligomers, diethylene glycol (DEG), metal oxide catalysts, typically antimony oxides and traces of other compounds. EG containing impurities is hereinafter referred to as spent glycol. The presence of impurities in the waste glycols can adversely affect product quality and thus prevent recycling of the waste glycols into the first stage. In particular, when a product with little or no color is required, the waste glycol is unsuitable for recycling.

Prior art for waste glycol recycling mainly relies on flash distillation of spent glycols typical of US Pat. Nos. 3,408,268, 3,367,847 and 2,788,373. There are a number of modifications to the basic distillation process. For example, US Pat. No. 3,878,085 teaches flash distillation of spent glycols in the presence of alkali metal hydroxides, while US Pat. No. 3,491,161 teaches adding ammonium hydroxide before distillation. . Several attempts have been made to precipitate anti-glycols prior to distilling the waste glycols. Typical of such methods are described in US Pat. Nos. 4,118,582 and 4,013,519.

In practice, spent glycols are purified by distillation where pure EG overhead products are recovered. Typically purified EG is commercially available in the antifreeze market. At the bottom of the distiller produced by the type of waste glycol is a mixture of antimony oxide catalyst, terephthalate oligomer, EG and DEG and various trace impurities such as trace cations, trace anions and colored impurities.

Seriously, every year in the United States a large amount of distillation bottom material is produced, which is a serious environmental and economic problem for PET manufacturers. In addition, the disposal of the stills bottoms as waste all means the loss of significant commercially valuable amounts of EG, DEG, antimony catalysts and terephthalate oligomers.

Therefore, there is a need for a method for removing impurities from waste glycols and for recovering and recycling stills bottoms. In particular, enhanced methods are preferred where all materials are recycled to the PET manufacturing process or other chemical manufacturing processes.

[Initiation of invention]

The present invention relates to a method for recovering EG from waste glycols produced in the production of polyethylene terephthalate (PET), comprising terephthalic acid or lower alkyl esters [eg; Dimethyl terephthalate (DMT)] and EG react to form dihydrooxyethyl terephthalate (DHET), and DHET is polymerized in the presence of a metal oxide catalyst (e.g. antimony oxide) to reduce PET and metal oxide catalyst residues, low molecular weight It is an enhanced process that forms waste glycols containing terephthalate oligomers, diethylene glycol and other trace impurities, EG is recovered by fractional distillation, antimony catalysts are recovered, and terephthalate oligomers are recovered for recycle. Ion exchange resins are only suitable for the purification of ionic contaminant-containing liquids. However, waste glycols are not suitable for direct introduction into the ion exchange layer due to the presence of low molecular weight solid oligomers in waste glycols at or about room temperature. This solid can be removed by filtration but results in economically unsatisfactory product loss. As mentioned above, some prior art solutions to solve this problem rely on the introduction of a factor that dissolves the solid polymer. The enhanced method of the present invention increases the solubility of low molecular weight oligomers by increasing the temperature of the waste glycols so that the low molecular weight oligomers can be dissolved in EG, and furthermore, the lungs without adversely affecting the performance of the ion exchange resin at elevated temperatures. It is based on the principle that glycol can pass through the ion exchange layer.

The enhanced process involves raising the temperature of the waste glycol to 50 to 160 ° C. to dissolve the low molecular weight ethylene terephthalate oligomer (a) [The required temperature depends on the amount of low molecular weight oligomer in the waste glycol. Higher temperature is required to dissolve lower molecular weight oligomers at higher concentrations; (b) separating residual insoluble material from waste glycol (b), passing the waste glycol through activated carbon at 50 to 160 캜; (C) removing the dissolved colored impurities by passing the waste glycol through a cation exchange resin at a temperature of 50 ° C. to the maximum temperature the resin can tolerate to remove the antimony compound and other trace cations that may be present. (E) passing the waste glycol through an anion exchange resin at a maximum temperature that the resin can tolerate to remove impurities such as phosphate and acetate (e), passing the waste glycol through a cation / anion exchange resin mixture to Step (f) of removing the impurities and optionally distilling the waste glycol to recover the relatively pure EG, DEG and terephthalate. And a step (g).

The aforementioned method can be further enhanced by recovering antimony after acid regeneration of the cationic resin. The antimony salt obtained can then be recycled for use in the flame retardant industry and other common end uses.

An equivalent method as another aspect of the present invention can be used for the recovery of EG, DEG terephthalate oligomers and antimony catalyst from the distillate bottoms produced during EG recovery by waste glycol distillation. In another embodiment, the stills bottoms are first mixed with EG in an amount sufficient to dissolve the low molecular weight terephthalate polymer while raising the temperature of the waste glycol as indicated in the enhanced process described above.

[Brief Description of Drawings]

1 is a block flow diagram of the method of the present invention to be performed for recovery of waste glycols.

2 is a block flow diagram of the method of the present invention to be carried out for recovery of the stills bottoms.

Best Mode of the Invention

The present invention is suitable for recovering ethylene glycol, diethylene glycol, antimony and terephthalate polymers from PET manufacturing processes. The waste glycols obtained from the PET process are typically 90 to 99% EG, 1 to 5% DEG, 1 to 10% low molecular weight terephthalate oligomer, 0.01 to 5% antimony, 2 to 5% water, It contains traces of other metal ions and traces of phosphates, acetates and other anions as well as other contaminants.

The low molecular weight terephthalate oligomer is dissolved in EG by raising the temperature of the waste glycol to about 50 to about 160 ° C. and maintaining at this temperature for a period sufficient to completely or nearly completely dissolve the low molecular weight terephthalate oligomer solid. Some solids can be uneconomical to dissolve and can be removed by filtration. Referring to FIG. 1, waste glycols obtained from the PET process accumulate in the storage tank 1, from which they are transferred to a steam heated bath 3 by a pump 2. For the application of high molecular weight ethylene terephthalate polymers to dihydroxyethylene terephthalate (DHET) and other low molecular weight terephthalyl esters, the reaction can be carried out in a pressure bath at elevated temperatures above the boiling point of EG at atmospheric pressure. The temperature and time required for dissolution of the low molecular weight oligomer depends on the amount of low molecular weight oligomer present initially.

The solution of waste glycol and depolymerized PET may contain small amounts of insoluble matter. Insoluble matter is removed by pumping the solution using a pump 4 through a suitable filtration medium 5 to remove particulates. In the process of the invention, it is desirable to maintain the fluid temperature at about 50 to about 160 ° C. to produce a low viscosity solution at low pressure drop during filtration and to eliminate the possibility of precipitation of terephthalate oligomers. The filtration medium 5 can be selected from a number of conventional types such as bags, cartridges or tubular filters, provided that they are compatible with the EG and that the pore size is small enough to remove particulate matter in the waste glycol.

A solution of waste glycol is passed through the activated carbon layer 6 to remove traces of colored contaminants, if present. In the process of the invention, it is preferred to maintain the waste glycol at about 50 to about 160 ° C. in the activated carbon layer 6. Although other adsorbents are used, activated carbon is the preferred adsorbent for removing colored impurities. It is preferable to remove the dissolved solid leached from the activated carbon with the ion exchange resins (7), (8) and (9) using the activated carbon layer (6) before the ion exchange resins (7), (8) and (9). Do.

Soluble metal oxide catalysts, typically antimony compounds, present in the spent glycols are removed by ion exchange with strong or weak acid cation exchange resins (7). The strong acid cation resin selected may be ResinTech CG8, Rohm Haas IR 120, Ionac C-249, Purolite C100 or similar type. When the weak acid cation resin is selected, it may be Resintech WACMP, Rohm and Haas IRC-84, Ionak CC, Purolite C-105 and the like. In the process of the present invention, it is preferable to pass the waste glycol through the cation exchange resin 7 while maintaining the temperature at about 50 ° C. to the maximum temperature the resin can withstand. Cationic resins having an allowable temperature of 85 ° C. or lower and anionic resins having an allowable temperature of 60 ° C. or lower are known in the art. However, the method is not limited to the maximum temperature that a resin of the art can withstand, which is intended to extend the scope of the invention to a resin which is then resistant at higher temperatures. However, low temperatures are preferred to exclude reducing the life of the resin to an unacceptable extent. Once the cation exchange resin is consumed, that is, if antimony or other cationic impurities are present in the effluent stream at unacceptable concentrations, the antimony is removed by passing strong mineral acids (eg hydrochloric acid or sulfuric acid) through the cation exchange resin. Typical acid concentrations are 5-25 weight percent. The amount of acid regeneration may be 10 to 30 lb of acid per 1 ft ³ of resin.

Depending on the type of acid regeneration used, various forms of antimony can be recovered. For example, when HCI is used, SbCl ₃ is in the recovered antimony form. Antimony trioxide (Sb ₂ O ₃ ) is widely used as a flame retardant for plastics, wastes, rubbers and textiles in principle. Antimony recovered from the process as antimony trichloride can be converted to antimony trioxide by adding water to the regeneration solution. In addition to being used as a flame retardant, antimony trioxide is suitable for recycling antimony tablets.

After removal of the antimony compound, the spent glycol is passed through an anion exchange resin 8 to remove soluble anions such as phosphate and acetate. Some antimony catalysts may be in the form to be removed by anion exchange resin. Antimony is considered amphoteric in that it can act as a weak acid or weak base to exist in cation or anionic form. The anion exchange resin 8 may be strong base type (I) or type (II). The selected type (I) strong base anion resin may be Resintech SBR, Rohm and Haas IRA-400 or 402, Ionak ASB1 or ASBIP, Purolite A-400 or 600. Type II strong base anion resins can be Resin Tech SBG2, Rohm and Haas IRA-410, Ionak ASB2, Purolite A-300, and the like. Weak base anion resins are required for phosphate removal. In the process of the present invention, it is preferred to pass the waste glycol through anion exchange resin 8 while maintaining the temperature of about 50 ° C. to the maximum temperature the resin can withstand. When the anion exchange resin (8) is consumed, the resin is regenerated with a strong base (eg caustic soda (NaOH)). Typical soda concentrations are 6-10% and NaOH per 1 ft ^{3 of} resin is added at a regeneration addition rate of 4-15 lb.

The waste glycol can be further purified by passing the glycol through the mixed cation / anion resin 9. The resin selected may be the resin described above. It is preferable to use mixed cation / anion resin 9 for complete removal of soluble impurities. In the method of the present invention, it is preferable to maintain the temperature of the waste glycol in the mixed layer resin at about 50 ° C. to the maximum temperature that the resin can withstand.

In some cases, the treated EG can be recycled directly to the PET manufacturing process. In many cases, the presence of small amounts of impurities that cannot be removed will have a decisive impact on product quality. There is actually a small amount of diethylene glycol (DEG). DEG may be acceptable without causing product quality problems in some PET polymers. Since the process of the present invention removes traces of cations and anions as well as colored impurities, the treated EG can be directly recycled without distillation for DEG removal. Distillation to separate DEG into EG is also a method in the art.

Another aspect of the process can be used for recovery of stills bottoms. Another process is described with reference to FIG. The distillate bottoms are first mixed with EG sufficient to dissolve the solid low molecular weight terephthalate oligomer while raising the temperature of the mixture in reactor 10 as described in the recovery process of the waste glycol. From this the process proceeds as described in the preferred embodiment of the present invention as described in FIG.

Although the present invention has been described with reference to various preferred alternative embodiments, it is not intended to be limiting and should be regarded as a typical illustration, the scope of the invention being limited as set forth in the appended claims.

Claims (31)

Sufficiently raising the temperature of the waste glycol to dissolve the low molecular weight terephthalate oligomer (a), passing the waste glycol through an ion exchange medium capable of removing the metal oxide catalyst at elevated temperature (b), and distilling the waste glycol Recovering ethylene glycol, diethylene glycol and terephthalate oligomers to form a dihydroxyethyl terephthalate by reacting terephthalic acid or dimethyl terephthalate with excess ethylene glycol to form dihydroxyethyl terephthalate. In the polyethylene terephthalate production process, the phthalate is polymerized in the presence of a metal oxide catalyst to form polyethylene terephthalate with waste glycols containing metal oxide catalysts, cationic impurities, anionic impurities, low molecular weight terephthalate oligomers, ethylene glycol and diethylene glycol. A method for recovering ethylene glycol from the produced waste glycol. The method of claim 1 wherein the temperature of step (a) is from about 50 ° C. to about 160 ° C. 7. The process of claim 1 wherein the distilled ethylene glycol recovered in step (c) is recycled in the manufacturing process. The method of claim 1, wherein the waste glycol contains colored impurities, and further comprising, prior to step (b), passing the waste glycol through activated carbon at elevated temperature. The process of claim 1, further comprising, immediately after step (a), the waste glycol after step (a) contains an insoluble material and the waste glycol is passed through a filtration material capable of removing the insoluble material at elevated temperature. Way. The process of claim 1 wherein the ion exchange medium of step (b) comprises a cation exchange resin to remove metal oxide catalyst and cationic impurities. The method of claim 1 wherein the ion exchange medium of step (b) comprises an anion exchange resin to remove metal oxide catalyst and anion impurities. The process of claim 1 wherein the ion exchange medium of step (b) comprises both a cation exchange resin and an anion exchange resin. The method of claim 1 wherein the waste glycol after step (b) contains trace anions, trace cations and trace other impurities, and passing the waste glycol through a mixed bed ion exchange resin at elevated temperature after step (b). Including in addition to. 5. The method of claim 4, wherein the waste glycol after passing through the activated carbon contains trace amounts of cations, trace anions and trace amounts of other impurities, and the step of passing the waste glycol through a mixed bed ion exchange resin at elevated temperature after step (b) How to further include. 7. The process of claim 6 wherein the cation exchange resin is recycled by acid to recover the salt of the metal oxide catalyst after it is consumed. 8. The method of claim 7, wherein after the anion exchange resin is consumed, it is regenerated by alkaline reagents to recover the salts of the metal oxide catalysts. The method of claim 1 wherein the metal oxide catalyst is an oxide of antimony. The method of claim 6, wherein the metal oxide catalyst is an oxide of antimony. The method of claim 11, wherein the acid is hydrochloric acid. 8. The method of claim 7, wherein the metal oxide catalyst is an oxide of antimony. The method of claim 12, wherein the alkaline reagent is sodium hydroxide. The method of claim 15, wherein the metal oxide catalyst is an oxide of antimony. The method of claim 17, wherein the metal oxide catalyst is an oxide of antimony. Raising the temperature of the waste glycol to about 50 to about 160 ° C. to dissolve the low molecular weight terephthalate oligomer (a), and passing the waste glycol through activated carbon at about 50 to about 160 ° C. to remove colored impurities (b) (C) removing the metal oxide catalyst and other cationic impurities by passing the waste glycol through the cation exchange resin at a maximum temperature that the cation exchange resin can withstand (c) and the waste glycol (50) to the anion exchange resin Passing the anion exchange resin at the maximum possible temperature to remove the metal oxide catalyst and anion impurities (d), passing the waste glycol at about 50 ° C. to the mixed layer ion exchange resin at the maximum temperature that the mixed layer resin can withstand ( e) and distilling the waste glycol to recover ethylene glycol, diethylene glycol and terephthalate oligomer. For example, terephthalic acid or dimethyl terephthalate is reacted with excess ethylene glycol to form dihydroxyethyl terephthalate, and dihydroxyethyl terephthalate is polymerized in the presence of a metal oxide catalyst to form a metal oxide catalyst, cationic impurities, anionic impurities, A method for recovering ethylene glycol from waste glycols produced in a polyethylene terephthalate manufacturing process for forming polyethylene terephthalate with waste glycols containing colored impurities, trace impurities, low molecular weight terephthalate oligomers, ethylene glycol and diethylene glycol. The process of claim 20 wherein the distilled ethylene glycol recovered in step (f) is recycled to the manufacturing process. 22. The method of claim 21, wherein after step (a), the waste glycol contains an insoluble terephthalate oligomer and the waste glycol is passed through a filtration medium capable of removing the insoluble terephthalate oligomer at about 50 to about 160 ° C. (a) further immediately after. The method of claim 21, wherein the metal oxide catalyst is an oxide of antimony. 24. The process of claim 23 wherein the cation exchange resin is recycled by hydrochloric acid to recover antimony trichloride after the cation exchange resin is consumed. 24. The method of claim 23, wherein the cation exchange resin is regenerated by sodium hydroxide to recover sodium antimony after it is consumed. (A) adding ethylene glycol to the distiller bottoms in an amount sufficient to depolymerize the low molecular weight oligomers while raising the temperature of the bottoms of the distiller, and depolymerizing the low molecular weight terephthalate oligomers by sufficiently raising the temperature of the distiller bottoms. (b) passing the distiller bottoms at elevated temperature through an ion exchange medium capable of removing the metal oxide catalyst from the distiller bottoms and (c) distilling the bottoms of the distiller to produce ethylene glycol, diethyl glycol and low molecular weight Recovering the lephthalate oligomer, comprising the step (d): reacting terephthalic acid or dimethyl terephthalate with ethylene glycol to form dihydroxyethyl terephthalate and polymerizing dihydroxyethyl terephthalate in the presence of a metal oxide catalyst Ethylene glycol, diethylene glycol, From waste glycols containing low molecular weight terephthalate oligomers and metal oxide catalysts and polyethylene terephthalates, and from waste glycols providing distiller bottoms containing ethylene glycol, diethylene glycol, low molecular weight terephthalate oligomers and metal oxide catalysts Recovering ethylene glycol by distillation to recover ethylene glycol, diethylene glycol, metal oxide catalyst and polyethylene terephthalate from distillation bottoms produced by distillation of waste glycol formed in polyethylene terephthalate manufacturing process. 27. The process of claim 26, wherein step (c) further comprises recovering the salt of the metal oxide catalyst by regenerating the ion exchange medium. The method of claim 27, wherein in step (b) the temperature of the stills bottoms is raised from about 50 ° C. to about 190 ° C. 29. The method of claim 28, wherein the ion exchange medium of step (c) comprises a combination of a cation exchange resin, an anion exchange resin and a mixed bed resin. 30. The further step of claim 29, wherein after step (b) the stills bottoms contain an insoluble low molecular weight terephthalate oligomer and the stills bottoms are passed through a filtration mat that can remove the insoluble low molecular weight terephthalate oligomers. And after step (b). The method of claim 30, wherein the metal oxide catalyst is an oxide of antimony.